Down syndrome screening using race-specific femur length

Society for Maternal-Fetal Medicine Consult Series #57: Evaluation and management of isolated soft ultrasound markers for aneuploidy in the second trimester: (Replaces Consults #10, Single umbilical artery, October 2010; #16, Isolated echogenic bowel diagnosed on second-trimester ultrasound, August 2011; #17, Evaluation and management of isolated renal pelviectasis on second-trimester ultrasound, December 2011; #25, Isolated fetal choroid plexus cysts, April 2013; #27, Isolated echogenic intracardiac focus, August 2013)

Soft markers were originally introduced to prenatal ultrasonography to improve the detection of trisomy 21 over that achievable with age-based and serum screening strategies. As prenatal genetic screening strategies have greatly evolved in the last 2 decades, the relative importance of soft markers has shifted. The purpose of this document is to discuss the recommended evaluation and management of isolated soft markers in the context of current maternal serum screening and cell-free DNA screening options. In this document, "isolated" is used to describe a soft marker that has been identified in the absence of any fetal structural anomaly, growth restriction, or additional soft marker following a detailed obstetrical ultrasound examination. In this document, "serum screening methods" refers to all maternal screening strategies, including first-trimester screen, integrated screen, sequential screen, contingent screen, or quad screen. The Society for Maternal-Fetal Medicine recommends the following approach to the evaluation and management of isolated soft markers: (1) we do not recommend diagnostic testing for aneuploidy solely for the evaluation of an isolated soft marker following a negative serum or cell-free DNA screening result (GRADE 1B); (2) for pregnant people with no previous aneuploidy screening and isolated echogenic intracardiac focus, echogenic bowel, urinary tract dilation, or shortened humerus, femur, or both, we recommend counseling to estimate the probability of trisomy 21 and a discussion of options for noninvasive aneuploidy screening with cell-free DNA or quad screen if cell-free DNA is unavailable or cost-prohibitive (GRADE 1B); (3) for pregnant people with no previous aneuploidy screening and isolated thickened nuchal fold or isolated absent or hypoplastic nasal bone, we recommend counseling to estimate the probability of trisomy 21 and a discussion of options for noninvasive aneuploidy screening through cell-free DNA or quad screen if cell-free DNA is unavailable or cost-prohibitive or diagnostic testing via amniocentesis, depending on clinical circumstances and patient preference (GRADE 1B); (4) for pregnant people with no previous aneuploidy screening and isolated choroid plexus cysts, we recommend counseling to estimate the probability of trisomy 18 and a discussion of options for noninvasive aneuploidy screening with cell-free DNA or quad screen if cell-free DNA is unavailable or cost-prohibitive (GRADE 1C); (5) for pregnant people with negative serum or cell-free DNA screening results and an isolated echogenic intracardiac focus, we recommend no further evaluation as this finding is a normal variant of no clinical importance with no indication for fetal echocardiography, follow-up ultrasound imaging, or postnatal evaluation (GRADE 1B); (6) for pregnant people with negative serum or cell-free DNA screening results and isolated fetal echogenic bowel, urinary tract dilation, or shortened humerus, femur, or both, we recommend no further aneuploidy evaluation (GRADE 1B); (7) for pregnant people with negative serum screening results and isolated thickened nuchal fold or absent or hypoplastic nasal bone, we recommend counseling to estimate the probability of trisomy 21 and discussion of options for no further aneuploidy evaluation, noninvasive aneuploidy screening through cell-free DNA, or diagnostic testing via amniocentesis, depending on clinical circumstances and patient preference (GRADE 1B); (8) for pregnant people with negative cell-free DNA screening results and isolated thickened nuchal fold or absent or hypoplastic nasal bone, we recommend no further aneuploidy evaluation (GRADE 1B); (9) for pregnant people with negative serum or cell-free DNA screening results and isolated choroid plexus cysts, we recommend no further aneuploidy evaluation, as this finding is a normal variant of no clinical importance with no indication for follow-up ultrasound imaging or postnatal evaluation (GRADE 1C); (10) for fetuses with isolated echogenic bowel, we recommend an evaluation for cystic fibrosis and fetal cytomegalovirus infection and a third-trimester ultrasound examination for reassessment and evaluation of growth (GRADE 1C); (11) for fetuses with an isolated single umbilical artery, we recommend no additional evaluation for aneuploidy, regardless of whether results of previous aneuploidy screening were low risk or testing was declined. We recommend a third-trimester ultrasound examination to evaluate growth and consideration of weekly antenatal fetal surveillance beginning at 36 0/7 weeks of gestation (GRADE 1C); (12) for fetuses with isolated urinary tract dilation A1, we recommend an ultrasound examination at ≥32 weeks of gestation to determine if postnatal pediatric urology or nephrology follow-up is needed. For fetuses with urinary tract dilation A2-3, we recommend an individualized follow-up ultrasound assessment with planned postnatal follow-up (GRADE 1C); (13) for fetuses with isolated shortened humerus, femur, or both, we recommend a third-trimester ultrasound examination for reassessment and evaluation of growth (GRADE 1C).

Obstetric Ultrasounds in Africa: Is it Necessary to Promote their Appropriate Use?

This paper reviews the situation of obstetric ultrasound scans in Africa (extent of use, sonographer training, indications and results, etc.). Special emphasis is given to the advisability of legally regulating their use, the need for improved training among today's sonographers and the potential dangers that the incorrect and indiscriminate use of ultrasounds can involve. The paper condemns the commodification of the technique and reviews the current status of scientific production.

Evaluation of the usefulness of the fetal femur length with respect to gestational age to detect Down syndrome in Korean subjects

OBJECTIVE

We investigated the usefulness of shortening of the fetal femur length (FL) to predict Down syndrome at different gestational ages in Korean subjects.

METHODS

This study involved 110 Korean Down syndrome fetuses and 602 randomly selected euploid controls. The expected FL for any biparietal diameter (BPD) was calculated based on the control group data. Subjects were divided into four groups according to gestational age periods: 14-18 weeks; 19-23 weeks; 24-28 weeks and 29-36 weeks. The value of measured/expected FL ratio to predict Down syndrome was analyzed for each group.

RESULTS

The values of FL for any BPD in Down syndrome patients were significantly different from those in the control group (p < 0.001). A low ratio of measured/expected FL increased the risk of fetal Down syndrome (p < 0.001) with a mean measured/expected FL in Down syndrome of 0.907 (SD 0.075). At a fixed false positive rate of 5%, the sensitivities of FL were lower than 32.8% (95% CI 0.705-0.915) in three second trimester groups, and 71.1% (95% CI 0.924-0.997) in the third trimester group.

CONCLUSION

Short FL is a poor marker of Down syndrome in the second trimester in Korean subject. It may be used as a screening marker only in the third trimester.

Do race-specific definitions of short long bones improve the detection of down syndrome on second-trimester genetic sonograms?

OBJECTIVE

The purpose of this study was to determine whether the use of race-specific definitions of short femur and humerus lengths improves Down syndrome detection.

METHODS

This was a retrospective cohort study over 16 years. For each self-reported maternal race (white, African American, Hispanic, and Asian), we evaluated the efficiency of Down syndrome detection using published race-specific formulas compared with a standard formula for short femur and humerus lengths (observed versus expected lengths < or =0.91 and < or =0.89, respectively). The sensitivity, specificity, and 95% confidence intervals for each parameter were compared. Screening performance was compared by areas under the receiver operating characteristic curves.

RESULTS

Of 58,710 women, 209 (0.3%) had a diagnosis of a fetus with Down syndrome. Although the race-based formula increased sensitivity in each population, the increase was statistically significant only in the white population, whereas a decrease in specificity was statistically significant in all 4 populations, as denoted by nonoverlapping confidence intervals. The area under the receiver operating characteristic curve for the model using the race-specific definition of short femur length was 0.67 versus 0.65 compared with the standard definition, and for humerus length it was 0.70 versus 0.71.

CONCLUSIONS

The use of race-based formulas for the determination of short femur and humerus lengths did not significantly improve the detection rates for Down syndrome.

Variation in fetal ultrasound biometry based on differences in fetal ethnicity

OBJECTIVE

The objective of the study was to evaluate whether fetal ultrasound biometry is affected by variation in fetal ethnicity compared with white controls.

STUDY DESIGN

This was a retrospective observational study of ultrasound biometry in pregnant women with accurate gestational age.

RESULTS

Three hundred five white, 370 Asian, 895 part Hawaiian, 76 Pacific Islander, and 311 white Asian fetuses were analyzed. At 18 weeks gestation femur length was significantly shorter in Asian and white Asian. Humerus length was significantly shorter in Asian, part Hawaiian, and white Asian. White genetic sonogram was positive 14% for femur and 15% for humerus. The following was found: Asian 29% femur (odds ratio [OR], 2.58; 95% confidence interval [CI], 1.70-3.92), 25% humerus (OR, 1.86; 95% CI, 1.23-2.82); part Hawaiian 21% femur (OR, 1.67; 95% CI, 1.14-2.45), 23% humerus (OR, 1.64; 95% CI, 1.13-2.38); Pacific Islander 27% femur (OR, 2.37; 95% CI, 1.23-4.54), 33% humerus (OR, 2.76; 95% CI, 1.47-5.14); and white Asian 20% femur (OR, 1.56; 95% CI, 1.01-2.46), 22% humerus (OR, 1.56; 95% CI, 1.01-2.42).

CONCLUSION

Genetic sonogram was screen positive more frequently because of shorter long bone measurements in all nonwhite ethnicities.

Fetal age assessment based on 2nd trimester ultrasound in Africa and the effect of ethnicity

BACKGROUND

The African population is composed of a variety of ethnic groups, which differ considerably from each other. Some studies suggest that ethnic variation may influence dating. The aim of the present study was to establish reference values for fetal age assessment in Cameroon using two different ethnic groups (Fulani and Kirdi).

METHODS

This was a prospective cross sectional study of 200 healthy pregnant women from Cameroon. The participants had regular menstrual periods and singleton uncomplicated pregnancies, and were recruited after informed consent. The head circumference (HC), outer-outer biparietal diameter (BPDoo), outer-inner biparietal diameter and femur length (FL), also called femur diaphysis length, were measured using ultrasound at 12-22 weeks of gestation. Differences in demographic factors and fetal biometry between ethnic groups were assessed by t- and Chi-square tests.

RESULTS

Compared with Fulani women (N = 96), the Kirdi (N = 104) were 2 years older (p = 0.005), 3 cm taller (p = 0.001), 6 kg heavier (p < 0.0001), had a higher body mass index (BMI) (p = 0.001), but were not different with regard to parity. Ethnicity had no effect on BPDoo (p = 0.82), HC (p = 0.89) or FL (p = 00.24). Weight, height, maternal age and BMI had no effect on HC, BPDoo and FL (p = 0.2-0.58, 0.1-0.83, and 0.17-0.6, respectively). When comparing with relevant European charts based on similar design and statistics, we found overlapping 95% CI for BPD (Norway & UK) and a 0-4 day difference for FL and HC.

CONCLUSION

Significant ethnic differences between mothers were not reflected in fetal biometry at second trimester. The results support the recommendation that ultrasound in practical health care can be used to assess gestational age in various populations with little risk of error due to ethnic variation.

Fetal age assessment based on femur length at 10-25 weeks of gestation, and reference ranges for femur length to head circumference ratios

BACKGROUND

The aim of the present study is to establish new reference charts for gestational age assessment based on fetal femur length (FL), and new reference ranges for FL to head ratios at gestational weeks 10-25, and to determine the effect of maternal and fetal factors on these charts.

METHODS

Six hundred fifty low-risk women with regular menstrual periods and singleton pregnancies were recruited to a prospective cross-sectional study after obtaining written consent. FL, outer-outer biparietal diameter (BPD), and head circumference (HC) were measured at 10-25 weeks of gestation. We used regression analysis in order to construct mean curves and to assess the effect of maternal and fetal factors on age assessment.

RESULTS

The new chart for age assessment by means of FL was based on 636 measurements. The 95% CI of the mean corresponded to <1 day. The variation between the mean and the 90th percentile was 5, 6, and 7 days at 13, 18, and 23 weeks, respectively, similar to the results when using BPD or HC. Maternal age modestly influenced gestational age assessment (1.3 days/10 years, P = 0.005), whereas smoking, height, body mass index, multiparity, fetal sex, cephalic index, and breech presentation had no impact. Reference charts for FL to head ratios have been presented. Maternal age, fetal sex, and cephalic index influenced the FL/BPD ratio, whereas only fetal sex influenced FL/HC.

CONCLUSIONS

Fetal age assessment based on FL is an equally robust method as using HC. FL/HC is a more robust ratio to characterize fetal proportions than is FL/BPD.